Based on the English alphabetical order, three of the following four letter-clusters are alike in a certain way and thus form a group. Which letter-cluster DOES NOT belong to that group?
(Note: The odd one out is not based on the number of consonants/vowels or their position in the letter-cluster.)

The correct option is ZZW.

To find the letter-cluster that does not belong to the group, let's analyze the pattern by looking at the numerical positions of the letters in the English alphabet:

A = 1, B = 2, C = 3, D = 4, E = 5, F = 6, G = 7, H = 8, I = 9, J = 10, K = 11, L = 12, M = 13, N = 14, O = 15, P = 16, Q = 17, R = 18, S = 19, T = 20, U = 21, V = 22, W = 23, X = 24, Y = 25, Z = 26

Let's check the pattern for each option:

1. UTR:
U = 21, T = 20, R = 18
Difference between 1st and 2nd letter: 21 - 20 = 1
Difference between 2nd and 3rd letter: 20 - 18 = 2
Pattern: -1, -2

2. IHF:
I = 9, H = 8, F = 6
Difference between 1st and 2nd letter: 9 - 8 = 1
Difference between 2nd and 3rd letter: 8 - 6 = 2
Pattern: -1, -2

3. NMK:
N = 14, M = 13, K = 11
Difference between 1st and 2nd letter: 14 - 13 = 1
Difference between 2nd and 3rd letter: 13 - 11 = 2
Pattern: -1, -2

4. ZZW:
Z = 26, Z = 26, W = 23
Difference between 1st and 2nd letter: 26 - 26 = 0
Difference between 2nd and 3rd letter: 26 - 23 = 3
Pattern: 0, -3

All letter-clusters except ZZW follow the pattern of subtracting 1 and then 2 from the alphabetical position of the previous letter. Therefore, ZZW is the odd one out.